This study explored the relationship between green space accessibility (GSA) in residential areas and adolescents’ mental well-being, and whether the relationship was moderated by sociodemographic factors (rainbow/LGBTIQ+ identity, disability, sex, ethnicity, neighbourhood deprivation) and perceived neighbourhood safety simultaneously. Data from 3813 adolescents who lived in Tāmaki Makaurau Auckland, Aotearoa New Zealand were drawn from the 2019 wave of the Youth2000 survey series. A Gaussian-based two-step floating catchment area method was employed to measure the spatial accessibility to green space at the neighbourhood level. Emotional well-being was assessed using the World Health Organization-5 Well-being Index and depressive symptoms were measured using the Reynolds Adolescent Depression Scale-short form. Through moderation analyses, results showed that perceived neighbourhood safety plays a vital role in the GSA – mental well-being association, with a negative trend in adolescents who reported being less safe in neighbourhoods. Adverse effects of GSA were found in rainbow, disabled, Asian and Pacific adolescents, under the condition of not feeling safe in neighbourhoods all the time. The results showed marginalised adolescents tended to feel less safe in neighbourhoods, have lower emotional well-being and a higher level of depressive symptoms. Additionally, there were inequalities in GSA for adolescents who lived in the most deprived neighbourhoods and adolescents of Māori ethnicity. This study provides novel evidence of the importance of safe and inclusive green space for effectively promoting mental health and mitigating health inequalities of adolescents in urban areas.